1. Field of the Invention
This invention generally relates to a geared hub. More specifically, the present invention relates to an internally geared hub for a bicycle that is configured to be mounted on a rearward portion of a bicycle frame and used as a rear wheel hub.
2. Background Information
Bicycles are typically provided with a chain drive that includes a rear drive sprocket mounted to a rear hub that is mounted to a rear portion of a frame of a bicycle. Some bicycles are provided with a rear hub that includes an internal gearing mechanism for shift among a plurality of gears to change an output gear ratio from a drive sprocket. This type of rear hub is often called an internally geared hub. One example of an internally geared hub is disclosed in Japanese Registered Utility Model Publication No. 3146138. The internally geared hub disclosed in this publication has a hub axle that is mounted to a rear portion of a bicycle frame, a hub shell that is arranged to rotate freely about the hub axle, a driver, a rotation transmitting mechanism with a planetary gear mechanism and a gear changing mechanism. The driver is mounted between the hub axle and the hub shell such that it can rotate freely relative to both the hub axle and the hub shell. The planetary gear mechanism of the rotation transmitting mechanism transmits rotation of the driver to the hub shell through one of a plurality of gears (gear ratios). The gear changing mechanism shift among (i.e., select one of) the gears of the rotation transmitting mechanism.
In the conventional internally geared hub presented in the aforementioned publication, a high gear among the plurality of gears transmits rotation of the driver directly to the hub shell. As a result, particularly in assisted bicycles having a motor to assist with pedaling, the service life of the high gear (which is used frequently) is increased, and thus, the service life of the entire internally geared hub can be increased. Additionally, the conventional internally geared hub is provided with a one-way clutch serving to transmit rotation of a carrier of the planetary gear mechanism to the hub shell only in a drive direction. As a result, when a rider is coasting without pedaling (e.g., on a downhill slope), the rotation of the hub shell is not transmitted to the driver and a torque is not transmitted to the pedals.